The present disclosure generally relates to in-vitro diagnostics and, in particular, to a method for carrying out heterogeneous chemical or biological reactions involving the use of analyte capturing particles.
In the field of in-vitro diagnostics, there is a need for the automated heterogeneous assay of chemical and biological samples. Due to several advantages such as, for example, low sample and reagent requirement, the possibility to integrate several assay steps into a single device, increased reaction kinetics, fast analysis times and hence high throughput, many efforts have been made to develop microfluidic systems in recent years.
Packed bed columns, built up as a pile of beads, have been commonly used, for example, in chromatography in chemical analysis for decades. Also in diagnostic applications, the use of porous frit structures is known in the art. For example, immunoassays on a rotating disc, where liquids flow through a packed bed column driven by centrifugal force, have been disclosed. Different ways of building columns with beads, or particles, in miniaturized systems are also known. A conventional way is to use slurries from which a fixed structure is obtained. Typically, a bead-liquid emulsion, or suspension, is flown through, along or over a chamber in which the beads are trapped. This trap can be either a small passage, such as a shallow slit, a porous material like a fleece or filter, for example, a sintered porous material, or larger beads. Another method is to trap the particles in a magnetic field. Typically, these methods all have the particles trapped in a forward flow direction in common. This means that the flow-resistance is fixed or increased when liquid is flown through. Due to an increased packing grade while trapping the particles, the column flow resistance will increase, possibly leading to clogging. When the column is used to bind molecules flowing through, this clogging effect can be more severe. In the case where the beads are trapped in a field, like for instance magnetic, the drag forces may exceed the trapping forces on the beads, resulting in bead loss. When single particles are packed in a geometrical way via a narrowed passage, the obtained pore-size depends on the bead-size. Because larger particles may not provide sufficient binding capacity, smaller particles are preferred but they will yield smaller pores and thus a higher flow resistance. As a consequence, there is a practical limitation of what bead-size can be used for a given flow pressure range. This can be a problem when, for instance, using centrifugation for driving the flow as the obtainable pressures are small. Once a column is clogged, it may be very difficult to recover it.